Fiber Reinforced Plastic (FRP) materials comprising a reinforced fiber and a matrix resin have excellent mechanical properties such as strength and rigidity while being lightweight, and therefore are widely used as aircraft members, spacecraft members, automobile members, railway car members, ship members, sports apparatus members, and computer members such as housings for laptops, and the demand is increasing year by year.
In particular, FRP materials have been recently developed for industrial applications such as automobile members, windmill members and pressure container members. However, the costs of these current materials are too high for these applications due to the high cost of manufacturing and raw materials.
A resin transfer molding method is developed as a low cost manufacturing method. The resin transfer molding method is a method in which a reinforcing fiber base material is directly impregnated with a liquid thermosetting resin composition and cured. Since this method does not involve an intermediate product, such as a prepreg, it has great potential for molding cost reduction. However, FRP materials obtained by this method tend to have low strength and low stiffness due to low fiber content.
The prepreg lamination and molding method can prepare FRP materials having excellent mechanical strength and stiffness. The prepreg lamination and molding method is a method in which a prepreg or prepregs, produced by impregnating a reinforcing fiber base material with a thermosetting resin composition, is formed and laminated, followed by curing of the resin through the application of heat and pressure to the formed and laminated prepreg/prepregs to obtain a fiber-reinforced plastic material.
Patent Documents 1 and 2 disclose matrix resins for the prepreg having a rapid curing property. However, FRP materials obtained from these have insufficient heat resistance for some of the painting processes for the automotive industry. Furthermore, minimum viscosities of these matrix resins are too high and the periods of times to achieve minimum viscosities (gel times) are too short. As the result, the flowability of the resins are insufficient in order to manufacture FRP materials having class A surface without complex cure cycles.
Patent Documents 3 discloses a matrix resin for the prepreg having a high Tg with certain cure cycles. However, because of the long gel times of the resin system the matrix resin will have too much flow from the prepreg, creating dry spots and resin starved areas on the surface of the FRP. This makes will make a FRP material without a class A surface.